Radiant floor extension to Hydronic Baseboard loop

Glenn Sossin_2

You might find the Roth Mini-Shunt a better choice - will allow you to use high temp water for the baseboard, while the unit itself mixes return with supply to get a much lower temp for your floor.

Good luck on your project.

Glenn

Chris Magee

Radiant floor extension to Hydronic Baseboard loop

I recently installed some 3/4" Thermapex for a hybrid baseboard / dry radiant floor installation for a small bathroom remodel project, approximately 40 sf of radiant floor heating area, about 80 lf of PEX. I am attempting to mix my baseboard system with a dry radiant floor application, merely by cutting into and/or bypassing the peripheral baseboard 3/4" copper line and connecting to the 3/4" PEX. The PEX will lay on the floor (slab on grade) to heat the air cavity between my slab/ floor furring (1-1/2") and subsequently radiate through 1" of cement backer board and cement finish board.

I thought it might make sense to put a valve at the PEX/ copper connection to be able to control water flow into the PEX loop in case its too hot or cold and let the peripheral copper maintain its run and this has opened up a researching 'can of worms' Alternatively, I am looking to just extend my loop into the PEX and let it run without any valves and simply let it be what I originally planned. Maybe that will work fine?

I have tested the temperature of the copper line/ fin tube at the spot I wish to connect the PEX and it is running about 150 F when the boiler is heating. I feel this will suffice for the floor to be warm and not overheated. I am also debating whether a reflective insulation on the existing slab may be of benefit or detriment towards over or under heating. Since my boiler runs at peak in the morning and night, it will not be on the duration of a normal radiant floor system.

I have thoroughly read this article:

http://www.heatinghelp.com/heating_howcome3.cfm

regarding using diverter valves which seems to be applicable to my condition. My problem comes with trying to figure out how to have some control over the amount of water that goes into my radiant floor while still maintaining my current baseboard water flow and how exactly to set this up in the simplest manner. Could I use a thermostatic valve or some other simple valve (where the control knob could be exposed through the finish) to control my new radiant floor extension? This way if its too hot I can turn it down as I'm mostly concerned with overheating and also static pressure. FYI, my system has 3 loops running off one pump, and currently everything runs/ heats just fine. Increasing the pressure on one of these loops concerns me, but my pump is capable of pumping much more pressure. And when all the air is out of the system it would theoretically move all the water at the same rate?

So here are some questions:

Does anyone think the concept will work and not overheat the floor?

Should I use one or two diverter valves?

Would a Thermostatic valve want to be in the main 3/4" copper pipe between the two tees instead of the branch piping, thus eliminating the need for diverter tees, in essence, when I want heat I would control the valve?

First time using this forum, so many thanks in advance to any advice. Also I have attached a small PDF diagram of the issue.

Thanks,
Chris

Al Letellier_9

radiant add on

You definitely need to mix that temperature down for the radiant. 150 is way too hot. You should have a heat loss done to determine proper flow rate and temperature for the size of the room. You can use a "in the box" mixing station as mentioned in the previous post or use a separate mixer and circulator. This is NOT a DIY job if you want it done right.

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Chris Magee

Radiant floor extension to Hydronic Baseboard loop

A couple considerations in looking at 'mixing' the water temperature down. First I'm heating an air cavity and won't have any conduction, there's no aluminum plates to help the heat transfer. Additionally I'm heating 1" of cementitious material (2 layers 3/8" bacckerboard & 1/4" of cement board). From everything I have researched a higher water temperature is needed for this type of application, for example, I've seen applications where having to heat the air cavity of a floor and going through padding and carpet the recommended water temp is 140-160 F.